Fixture, prosthesis anchoring device and prosthesis

ABSTRACT

The invention is related to an arrangement used to attach a prosthesis to one or more fixtures ( 1 ) anchored in a person&#39;s bone tissue. Such a fixture ( 1 ) has a fastening part ( 8 ) for the prosthesis and said fastening part has a supporting surface the prosthesis and a said fastening part has a supporting surface ( 9 ) that engages a bearing surface ( 13 ) on the prosthesis. In accordance with the first aspect of the invention such a fixture ( 1 ) on its supporting surface ( 9 ) is provided with a deformation device ( 18 ). This is plastically deformable in a direction perpendicular to supporting surface ( 9 ) to compensate for any misalignment between supporting surface ( 9 ) and bearing surface ( 13 ). In accordance with a second aspect of the invention, the deformation device is, instead, arranged on the prosthesis supporting surface ( 13 ) in a corresponding way. The invention also incorporates a prosthesis anchoring system that includes a fixture having a deformation device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fixture for implantation andosseointegration with bone tissue whose purpose is to carry aprosthesis, a prosthesis anchoring system, and a prosthesis attached tothe fixture.

2. Description of the Related Art

It is known to implant fixtures in a person's bone tissue in order toattach different types of prostheses to them, dental prostheses forexample.

To make certain that the fixture anchorages are permanent, a number offactors must be fulfilled with regard to, among other things, materialselections and operation techniques. In practice, fixtures developed byProfessor Branemark made of pure titanium with micro-pitted surfaceshave shown very good long-term anchoring abilities. The screw-shapedfixtures are operated into a bone, the jawbone for example, and arepermitted to heal in -osseointegrate—for a certain time period, usuallya few months. Thereafter, a prosthesis can be mounted on the fixtures.

Most types of these fixtures are provided with external threads—and arethus implanted screws—and they are attached by screwing them into holesmade in the bone tissue. The holes are often pre-threaded, but it isalso possible to screw in self-tapping screws. Normally, the fixturesrequire shorter or longer times for healing-in before they should beexposed to significant loads. On the fixtures, one can attach differenttypes of prostheses, and for dental prostheses one can attach individualteeth, i.e., one tooth per fixture, but it is also possible for two ormore fixtures to serve as attachment points for a bridge structurecontaining a number of teeth or even an entire row of teeth. Thefixtures are therefore designed in a suitable way at their free ends.

The free end of such a fixture to which a prosthesis is to be fastened,i.e., the fastening end, is equipped with some form of fastening devicethat will engage a corresponding fastening device on the prosthesis. Itis herewith usual to have the attachment arranged so that a bearingsurface on the prosthesis or a prosthesis-carrying element will be incontact with a supporting surface on the fixture's fastening end. Thesupporting and bearing surfaces should be parallel to ensure fullysatisfactory functionality. This seldom poses any problem for prosthesesof the type that are attached by means of only one fixture since in suchcases the prosthesis, which is usually fastened by a threaded joint tothe fixture, will have its bearing surface forced into contact with thefixture's supporting surface throughout its entire area when theprosthesis is screwed into place.

In many cases, a prosthesis can be anchored using more than one fixture.This is especially true in connection with jaw reconstruction when aprosthesis containing a row of teeth is to be attached, but it can alsooccur for prostheses used for other parts of the body.

When such a prosthesis or a holder for such a prosthesis is to beattached to two or more fixtures, the fixture onto which the prosthesisis first attached and screwed into place will force the prosthesis intoa certain position as a result of the fact that its bearing surface,which is pressed against the fixture's supporting surface will forciblyhave its direction determined by said supporting surface. For screwing aprosthesis to the second fixture and to additional fixtures if any, itis desirable that the corresponding bearing and supporting surfaces onthis/these fixture(s) also be parallel so that there will be nomisalignment. When anchoring fixtures in bone tissue one tries, ofcourse, to have the supporting surfaces assume their intended directionsrelative to each other with the greatest possible precision, and thesedirections should be adapted to the corresponding bearing surfaces onthe prosthesis. Usually the fixture surfaces are to lie in the sameplane or at least be parallel.

To fully achieve this is very difficult, and it must be expected that ananchored fixture will deviate directionally from what is intended.Anchoring two or more fixtures fully parallel is also very difficult,and the possibility of obtaining precisely matching heights is remote. Adeviation of even a mere degree or so results in a deficient fit betweenthe supporting surfaces and bearing surfaces when a prosthesis, asdescribed above, is attached to the fixtures. Since the prosthesiselement or prosthesis holder is generally made from a completely rigidmaterial such as stainless steel, a faulty fit cannot be compensated forby deforming the element or holder. Instead, there is poor contact withone or more of the fixtures' supporting surfaces and strains develop inthe prosthesis structure when one tightens the threaded joint to attachthe prosthesis to the fixtures. Moreover, these strains are propagateddown into the bone tissue. This can cause discomfort and trouble for thepatient while detracting from the functionality of the prosthesis andshortening its life expectancy.

This problem is especially common in connection with jaw reconstructionwhere a superstructure with a dental prosthesis is screwed in place onthe fixtures directly or via an attachment bar. Such a lack ofparallelism among the fixtures poses a major problem, particularly inconnection with the use of prefabricated superstructures not intendedfor extensive individual adaptation. In order to compensate for thisnon-accuracy it is earlier known e.g. from EP 0126 624, EP 0370 590 andEP 0466 267 to provide an intermediate elastic device between thefixture and the prosthesis.

SUMMARY OF THE INVENTION

The present invention eliminates the disadvantages described above thatare encountered when the directions of the fixtures and/or their heightpositions do not fully match what was intended, and without insertingspecial compensation elements.

In accordance with the invention, this has been achieved by means of afixture for implantation and osseointegration with bone tissue whosepurpose is to carry a prosthesis, by means of a prosthesis anchoringdevice having a prosthesis base that engages the fixture, and by meansof a prosthesis containing a number of attachment units arrangedintegrally with the prosthesis or with a separate prosthesis base, whereeach attachment unit is arranged to be attached to a fixture anchored ina person's bone tissue, and also containing a bearing surface arrangedso that when the prosthesis is attached to said fixtures, the bearingsurface will be in contact with a supporting surface on the appropriatefixture, the bearing surface and the supporting surface both beingsubstantially perpendicular to a center axis of a related fixturewherein at least one of said bearing surfaces is provided with adeformation device that is deformable in at least one direction that isperpendicular to bearing the surface to attain absolute parallelitybetween the supporting surface and the bearing surface when the bearingsurface is pressed against the supporting surface.

Because the supporting surface on the fixture or the bearing surface onthe prosthesis is integrally provided with a deformation device that canbe deformed plastically in a direction perpendicular to the respectivesurface when misalignment occurs, the deformation device will bedeformed to a corresponding extent. As a result, the bearing surfacewill have a fully functional contact with the supporting surface inspite of the misalignment. Since angular misalignment is absorbed bysuch deformation devices, the tightening of the retainer screws will notimplement any strains in the patient's bone tissue.

The fixture is preferably designed with at least parts that arerotationally-symmetrical, wherewith its supporting surface isperpendicular to its center axis.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

In one preferable embodiment, the deformation device is designed as anaxially aligned flange, suitably cylindrical and coaxial with the centeraxis.

It is preferred that the flange be peripherally arranged on a circularsupporting surface to provide optimal deformation distribution. Thiswill occur as a result of the fact that the flange will then be locatedat as long a distance as possible from the center axis.

In other preferred embodiments, the flange is provided with slots and/oris beveled axially outward, thereby facilitating deformation.

Moreover, it is preferred that the flange's outer end be pointed, i.e.sharp, thus providing progressive resistance to deformation.

The above and other preferred embodiments of the invention are set forthin the dependent claims.

BRIEF DESCRIPTION OF THE DRAWING(S)

The invention is explained in greater detail in the following detaileddescription of one preferred embodiments of the invention withreferences to the accompanying figures, of which:

FIG. 1 presents a rough sketch of the known technique.

FIG. 2 is a partially sectioned side view of a fixture in accordancewith the first embodiment.

FIG. 3 is a perspective view of a part of the fixture shown in FIG. 2.

FIG. 4 is an enlarged section taken through a part shown in FIG. 3.

FIGS. 5-7 are sections that correspond with what is shown in FIG. 4,illustrating the second through the fifth embodiments of the invention.

FIG. 8 is an end view of a fixture in accordance with a sixth embodimentof the invention.

FIG. 9 is a perspective view of a part shown in FIG. 8.

FIG. 10 is an exploded view of a prosthesis anchoring device inaccordance with the invention.

FIG. 11 is a longitudinal section taken through a part shown in FIG. 10.

FIG. 12 is a side view of a part in a prosthesis in accordance with theinvention.

FIG. 13 is an end view of a part shown in FIG. 12.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The purpose of FIG. 1 is to clarify the set of problems that the presentinvention is intended to solve, and it is therefore drawn in schematicform. 101 represents a part of a prosthesis, a bridge base for a dentalbridge for example. Prosthesis part 101 is anchored in a person'sjawbone by means of a number of fixtures screwed into holes made in thejawbone. Only two fixtures 102, 103 are shown in the figure, and onlytheir upper ends are shown. Each fixture acquires a direction determinedby the hole in the jawbone in which it is anchored. Quite frequently,these holes are not fully parallel, which leads to corresponding mutualmisalignment of fixtures 102, 103. Prosthesis part 101, when it istightened against the first fixture, is forced into a positiondetermined by the direction of the first fixture's supporting surface104 when the corresponding bearing surface 105 on prosthesis part 101 isdrawn into contact with supporting surface 104.

If, then, the second fixture 103 has an angular deviation fromparallelism with the first fixture 102, the tightening of the threadedjoint located at the second fixture 103 will lead to a misalignment ofthe second fixture's supporting surface 106 relative to thecorresponding bearing surface 107 on the prostheses part so that contactwill be almost of the point-to-point type, as shown at 108. When bothfixtures are tightened against prosthesis part 101, torque will bedeveloped on each fixture in the directions shown by the arrows. Suchtorque will create strains in the jawbone where the fixtures areanchored. The harmful effects of this are mentioned in the introductionto the description. Similar problems are encountered if the positions ofthe fixtures' bearing surfaces do not match with regard to height.

FIG. 2 shows a fixture1 according to the present invention with itsanchoring end anchored in a person's lower jawbone 2. At the upper endof fixture 1, its fastening end, there is a base such as a bar 3intended to carry a dental prosthesis bridge (not shown) attached to it.

Fixture 1's anchoring part 7 is conventionally designed with a threadedpart 4 which, at its end, has a conical part 5 provided with slots 6.Anchoring part 7, which is made of titanium, is self-tappingly screwedinto a pre-drilled hole in jawbone 2. The upper end, the fastening end,of the fixture, comprises a spacer part 8 which can be combined withanchoring part 7 to form a single piece or more commonly, arranged as aseparate unit that is screwed into an anchoring part 7 that has beenprovided with an internally threaded bore (not shown in FIG. 2).

The fastening end is provided with an attachment unit that engagesanother attachment unit adapted to it on bar 3, whereupon the two areattached together. The fastening end's attachment unit contains asupporting surface 9 arranged perpendicularly to the fixture'slongitudinal axis A, an axially aligned projection 10 extending out fromsupporting surface 9, the projection having a hexagonal outer profile,and an internally threaded bore 12 in the fixture that is axiallyaligned relative to the top of the projection. Bar 3's correspondingattachment unit contains a section of its bottom surface that comprisesbearing surface 13, a through-going bore 14, a cylindrical countersink15 at the upper end of the bore, a hexagonal countersink 16 at the lowerend of the bore and a retainer screw 17.

Bar 3 defines a direction that is dependent on the direction of a first(not shown) fixture as described in connection with FIG. 1. As mentionedpreviously, an effort is made to see that this direction's normalalignment B will correspond to the shown direction A of fixture 1. Suchis not the case in the figure. Instead, there is an angular deviation ofa° between them. A corresponding angular deviation also occurs betweensupporting surface 9 and bearing surface 13.

The bearing surface 9 is provided with a deformation device in the formof a flange 18 that is arranged at the periphery of bearing surface 9and extends axially out from it. The flange is relatively thin, about0.05 mm, and has a height of about 0.15 mm. When fixture 1 is pulledfirmly onto bar 3 by tightening screw 17, the part of the fixture'ssupporting surface that consists of the flange will come into directcontact with bearing surface 13 on bar 3. Since the surfaces are notparallel, contact occurs initially at a single point on flange 18.Continued tightening of the screw deforms flange 18 at this location,and when the screw is tightened further, this deformation extendsthroughout more and more of flange 18. Because the deformation isplastic, the change in shape is retained. The left side of the figureshows the flange deformed in this way at 19. The deformed flange willacquire an end surface that is parallel with bearing surface 13 on bar3, and contact it throughout its entire extent. Compensation has thusbeen obtained for angular deviation a so that there is good contactbetween fixture1 and bar 3 and so that no strains develop in jawbone 2.

FIG. 3 presents a perspective view of the upper end of fixture1. Thisalso shows how the fixture's spacer part 8 can be attached to itsanchoring part 7 by means of a threaded bore 20 represented by brokenlines that engages a corresponding threaded stud-end (not shown) onspacer part 8. This figure shows clearly how, at the upper end of spacerpart 8, an axial flange 18 provided at the periphery of supportingsurface 9 is shaped. This is also shown by FIG. 4, which shows a sectiontaken through the flange and drawn to a larger scale. Flange 18 is, inthis embodiment, uniformly thick and is terminated with a part that isperpendicular to the axial direction.

The embodiments shown in FIGS. 5 and 6 differ from what is shown in FIG.4 due to the fact that the outer ends of flanges 18 a and 18 b areprovided with a bevel 21 a, 21 b on their inner side and outer siderespectively. These bevels extend, in both cases, across the entirewidth of the flanges so that a pointed, i.e., sharp, edge is form at theouter end. The bevel can, of course, be arranged differently so that itextends over only a part of the width of the flange, leaving a flat edgesurface at the outer end of the flange. Similarly, the flange can beprovided with a bevel on both the inner and outer sides. Beveling keepsthe resistance to deformation relatively low when initial contact ismade. Resistance then increases more and more as the screw is tightened.

In FIG. 7, the deformation device comprises a flange 18 c which isradially aligned, wherewith a radially aligned circular slot 22 aroundspacer part 8 separates flange 18 c axially from the rest of spacer part8. Flange 18 c is deformed when pressure is brought to bear on a pointfarthest out on its top side, since it is then bent downward towardsslot 22 as indicated by the chain lines.

In the embodiment shown in FIG. 8, flange 18 e is provided with slots 23which facilitate deformation of flange 18 e. These are drawn to a largerscale in FIG. 9. Slots 23 can, as shown in FIG. 8, extend axiallythroughout the entire flange 18 e or, as shown in FIG. 9, extend onlythroughout a part of its axial extent. In the latter case, a lowerinitial deformation resistance is obtained.

FIG. 10 presents a dental prosthesis system for which the invention'sadvantages are of special importance. The dental prosthesis systemincludes a superstructure with a bridge 30 that is provided with dentalprostheses and a bar 4 to which bridge 30 is attached by means of anumber of screws 31 in threaded holes 32 in bar 4. Bar 4 is anchored ina person's jawbone via three fixtures1 to which bar 4 is attached bymeans of a number of screws 17, each of which is passed through a hole14 in the bar and screwed into a threaded bore in the appropriatefixture 1. Each fixture's supporting surface 9 will come into contactwith a corresponding bearing surface 13 on bar 4, and any angulardeviations will be taken up, in the manner described previously, byflange 18 which is shown in FIG. 11.

FIG. 12 is a side view of a bar 4′ which is of a type similar to thatpreviously described, but it shows an alternative embodiment of theinvention. Each of the individual bearing surfaces 13′ is locatedadjacent to a fastening hole 14′ on the bottom side of the bar. Eachbearing surface 13′ is provided with an axially aligned flange 18′ thatis concentric with fastening hole 14′. FIG. 13 shows, in an enlarged endview, how this flange 18′ is arranged. Flange 18′, in this embodiment ofthe invention, replaces the corresponding flange in the previouslydescribed embodiments. Here, deformation is absorbed by a deformationdevice on the bearing surface 13′ of bar 4′ instead of being taken up bysuch a device on the supporting surface of the fixture. In otherrespects, since the arrangement shown for this embodiment functions inthe same way as described previously, further description is omitted. Itshould be understood that the deformation device shaped as flange 18′ inthis embodiment can be modified in the different ways set forth for thepreviously described embodiments in which the deformation devices arelocated on fixtures.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A prosthesis support apparatus comprised of: abase for mounting a prosthesis a fixture including a bone-implantableanchor and a prosthesis attachment part, the bone anchor and theprosthesis attachment part forming an elongated unitary structure havinga central axis; the prosthesis attachment part including: a couplingelement operative to secure the base to the fixture; and an integralsupporting element including a planar surface substantiallyperpendicular to the central axis for engagement with a bearing surfaceon the base; the planar surface of the supporting element and thebearing surface being plastically deformable relative to each otherwhile the base is being secured to the fixture by the coupling elementsuch that the force applied by the bearing surface to the support iseffectively directed along the central axis when the base is fullysecured to the fixture.
 2. A prosthesis support apparatus as describedin claim 1, wherein the support element is plastically deformable suchthat the angle of the planar surface relative to the central axis isalterable while the base is being secured to the fixture by the couplingelement to compensate for misalignment between the base and the fixture.3. A prosthesis support apparatus as described in claim 2, in which thesupporting element is comprised of an axially extending flange with anaxially outer end thereof comprising the planar surface.
 4. A prosthesissupport apparatus as described in claim 2, in which the flange includesa plurality of transverse slots.
 5. A prosthesis support apparatus asdescribed in claim 2, in which the supporting element is comprised of anaxially extending annular flange with an axially outer end thereofcomprising the planar surface.
 6. A prosthesis support apparatus asdescribed in claim 5, in which the flange includes a plurality of radialslots.
 7. A prosthesis support apparatus as described in claim 2, inwhich the supporting element is comprised of an axially extending flangehaving a beveled axially outer end thereof comprising the planarsurface.
 8. A prosthesis support apparatus as described in claim 2, inwhich the supporting element is comprised of a radially extending flangehaving an axially upper face thereof comprising the planar surface.
 9. Aprosthesis support apparatus as described in claim 2, further includingan annular slot spaced from the axially outer end thereof, thus formingan annular flange, an axially outer face of the flange comprising theplanar surface.
 10. A prosthesis support apparatus as described in claim1, wherein the bearing surface on the base includes a plasticallydeformable portion such that the angle of the bearing surface relativeto the central axis is alterable while the base is being secured to thefixture by the coupling element to compensate for misalignment betweenthe base and the fixture.
 11. A prosthesis support apparatus asdescribed in claim 10, wherein the bearing surface is formed by anannular flange extending from the base and engageable with the planarsurface.
 12. A prosthesis support apparatus comprising: a base forsupporting a prosthesis device; a plurality of bone-implantableprosthesis support fixtures, each support fixture being comprised of: abone anchor; and a prosthesis attachment part, the bone anchor and theprosthesis attachment part forming an elongated unitary structure havinga central axis; the prosthesis attachment part including: a couplingelement operative to secure the base to the fixture; and an integralsupporting element including a planar surface substantiallyperpendicular to the central axis for engagement with a bearing surfaceon the base; the planar surface of the supporting element on each of thefixtures and the bearing surface of the base being plasticallydeformable relative to each other while the base is being secured to therespective fixtures by the coupling element such that the force appliedby the base to each of the fixtures is effectively directed along thecentral axes thereof when the base has been fully secured to all of thefixtures.
 13. A prosthesis support apparatus as described in claim 12,wherein the supporting elements are plastically deformable such that theangle of the planar surface relative to the central axis is alterablewhile the base is being secured to the fixture by the coupling elementto compensate for misalignment between the base and the fixture.
 14. Aprosthesis support apparatus as described in claim 13, wherein thebearing surface on the base is plastically deformable such that theangle of the bearing surface relative to the central axis of each of thefixtures is alterable while the base is being connected to therespective fixtures by the coupling element to compensate formisalignment between the base and the fixtures.
 15. A prosthesis supportapparatus as described in claim 14, wherein the bearing surface isformed by an annular flange extending from the base and engageable withthe planar surface.